1. Field of the Invention
The present invention relates to an image processing apparatus for performing a filtering operation such as an edge enhancement operation on a pixel signal.
2. Description of the Background Art
In digital still cameras, digital video cameras, image scanners and the like, various image processings are performed on inputted pixel signals. For example, an edge enhancement operation is performed by extracting high-frequency components from a pixel signal and adding the high-frequency components to the original pixel signal. Further, it is possible to remove noise from a pixel signal by applying an average filter or a median filter to the pixel signal.
When the edge enhancement operation is performed uniformly on pixel signals, however, there arises a problem of enhancing even noise components. Further, when a noise removal is performed by uniformly applying a low-frequency pass filter to the pixel signals, there arises a problem that the sharpness of edge components is deteriorated.
Then, conventionally performed is a method in which an edge component area is extracted from the pixel signals and a noise removal filter is applied to the area other than the edge component area. This method, however, has a problem that noise is left in an area in the vicinity of the edge components.
In International Publication 2006-043414, the applicant of the present invention shows a technique that the correlation direction of a pixel signal is judged and a pixel interpolation operation and a filtering operation related to the correlation direction are performed. Specifically, by using pixels in a direction where the correlation is high, the pixel interpolation operation and the filtering operation are performed. This technique produces an effect of achieving a sharp pixel signal.